A. Technical Field
The present invention relates to semiconductor wafers, and more particularly, to wafers having a diamond layer and a semiconductor layer including III-nitride semiconductor material and methods for fabricating the wafers.
B. Background of the Invention
Gallium Nitride (GaN) or AlGaN or AlN has electrical and physical properties that make it highly suitable for radio frequency (RF) devices, such as high electron mobile transistors (HEMT). In general, an RF device produces a large amount of heat energy during operation, requiring a mechanism to extract the heat energy from the device to avoid device failure. Diamond is known to have a good thermal conductivity and can be used as material for a substrate on which the AlGaN/GaN layer is formed.
One conventional approach to form a AlGaN/GaN HEMT layer on a diamond layer is depositing AlGaN/GaN HEMT layer directly on a silicon substrate, removing the silicon substrate and forming a diamond layer on the AlGaN/GaN HEMT layer. This approach is attractive for its low manufacturing cost. Also, the material property of silicon enables producing large silicon wafers with low surface roughness, which in turn enables producing large AlGaN/GaN HEMT wafers. In addition, the silicon substrate can be removed relatively easily by conventional wafer processing techniques. However there are still difficulties in growing a high-quality AlGaN/GaN layer directly on a silicon substrate due to the large lattice mismatch between AlGaN/GaN and silicon. As such, there is a need for methods for fabricating wafers that have a diamond layer and an AlGaN/GaN layer with enhanced material property.